Pressure-actuated switches

ABSTRACT

A pressure-operated electric switch, consisting of a housing having a spring loaded piston therein and a diaphragm moved by pressure change, with a microswitch having its operating pin coaxial with the piston and axially adjustable in relation to the piston, with the loading of the spring on the piston also adjustable independently of the pin to the piston.

United States Patent PRESSURE-ACTUATED SWITCHES 1 Claim, 4 Drawing Figs.

US. Cl 200/83 J,

200/82 C, 200/166 M Int. Cl H0lh 35/38 Field of Search ZOO/82.2,

[56] References Cited UNITED STATES PATENTS 2,898,418 8/1959 Byam200/166 M X 3,039,833 6/1962 Farkas... ZOO/82.2 X 3,419,692 12/1968Palen ZOO/82.2 3,444,341 5/1969 Mighton 200/822 3,412,223 11/1968 SchadPrimary Examiner-Robert K. Schaefer Assistant Examinerwilliam J. SmithAttorneys-Emory L. Groif and Emory L. Groff, .Ir.

ABSTRACT: A pressure-operated electric switch, consisting of a housinghaving a spring loaded piston therein and a diaphragm moved by pressurechange, with a microswitch having its operating pin coaxial with thepiston and axially adjustable in relation to the piston, with theloading of the spring on the piston also adjustable independently of thepin to the piston.

1g 3 1 f 5 16 H 16 a 7- 12 I 10 14L g 141 I 13 ii} 15 Fig.

I H l\ ZOO/153.19

PRESSURE-ACTUATED SWITCHES BACKGROUND OF THE INVENTION This inventionconcerns pressure-actuated switches, that is to say, switches which areactuated according to pressure changes, for example in a vessel orpressure system, which switches can be used as safety devices or asalarm switches or for control purposes, for example in instrumentationor automation.

An object of the invention is to provide pressure-actuated switcheswhich are of simple construction and which ensure a high degree ofaccuracy. Another object is to provide such switches which can be seteasily to operate at a predetermined pressure, or in which the pressurecan be adjusted within limits. A further object is to provide pressureswitches of robust construction in which there is no possibility of theelectric switch being damaged, for example by excessive overpressure.

SUMMARY OF THE INVENTION According to the invention, the switchcomprises a housing, a piston in said housing for axial movementtherein, a diaphragm held adjacent the head of said piston, an inlet forfeeding fluid pressure on to the diaphragm, a coil spring coaxial withthe piston to load same and the diaphragm against the pressure, asupport mounted on said housing, a microswitch carried by said supportwith its operating pin coaxial with the piston means for adjusting saidsupport axially in relation to the piston, means for adjusting thespring loading independently of the adjustment of the pin to the piston,and means for limiting movement of the piston towards the pin.

The construction according to the invention provides an arranger'nent inwhich the movement of the piston to operate the switch can be adjustedfinely and accurately, it being understood that the movement of amicroswitch operating pin for operation is small. Further, the inventionprovides a construction in which the limits of movement of the switchare accuratelyset, so preventing damage to the switch.

BRIEF DESCRIPTION OF THE DRAWINGS Reference will now be made to theaccompanying drawings, which show preferred embodiments of pressureactuated switches in accordance with the invention.

In the drawings:

FIG. 1 is a sectional elevation of one form of switch, which is presetand locked at the operating pressure.

FIGS. 2 and 3 are similar views of switches in which the operatingpressure can be adjusted within limits, and

FIG. 4 is a similar view of a switch which operates at subatmosphericpressure.

Like references indicate like parts in all of the views.

DESCRIPTION OF PREFERRED EMBODIMENTS Referring first to FIG. 1, thepressure switch consists of a bored stub 1 having a flange in forming ahead, the stub being externally screw-threaded at lb for securing to apressure vessel or pressure system. A housing 2 is secured to the flangehead 1a by means of a swaged over rim of the flange. Altematively and asshown in FIG. 3, the flange and housing could be secured together bybolts 4. A diaphragm 3 is secured between the flange and housing, aspacer ring 5 being interposed. The diaphragm conveniently is of nitrileor butyl rubber. A sealing ring 6 is also provided. The upper face ofthe diaphragm 3 is acted on by pressure in the vessel or system, and apiston 7 is provided in the housing, the top of which bears on or isattached to the lower face of the diaphragm.

The'piston can slide in .an upper cavity of the housing 2, its downwardlimit of movement being set by a shoulder or shelf 8 and its upper limitby abutment of the ring 5 cooperating with a shoulder 7a of the piston,the downward piston movement being opposed by a coiled spring 9. Thelower end of the spring bears on the bottom of a casing 10 screwthreaded on to the housing 2 at 11, so that axial adjustment of thehousing 2 and casing 10 can be made to adjust the spring loading. Theend of the piston extends through an aperture through the bottom of thecasing.

A microswitch 12 with an actuating or operating pin 12a is secured to asupport 13, which support 13 engages the casing 10 by screw threads 14.The switch is housed within a cover 15.

It will be understood that it is necessary for the accurate axialmovement of the pin 12a to be obtained, and that its total movement issmall, for example from its upward position it moves about 0.004 inch tochangeover, and further movement must not exceed about 0.001 inch. Theconstructions according to the invention permit accurate setting with nopossibility of excess pressure on the pin 12a.

The switch is adjusted by firstly screwing down the casing 10 to releasespring pressure on the piston, and the desired actuating pressure isthen applied through the stub I on to the upper face of the diaphragm.The casing 10 is then screwed up slightly (about 0.001 inch) and thesupport 13 is screwed up the casing 10 until the switch just operates bycontact with the lower end of its piston. The parts 2, l0, and 13 arethen locked up, for example by grub screws or by synthetic plasticinserts in the threads or by filling with epoxy resin.

In use, at suboperating or changeover pressure, the parts are in thepositions shown. As the pressure increases, the piston 7 moves. down andat the operating pressure the switch is operated. It will be seen thateven if this pressure is greatly exceeded', themicroswitch'can move downno more. than the amount by which the casing 10 was screwed uponadjustment, as the piston is stopped by the shoulder 8. Further, upwardspring pressure cannot damage the diaphragm as the shoulder 70 on thepiston, by abutment with the ring 5, limits upward piston movement.

In the construction shown in FIG. 2, after initial adjustment, theoperating pressure can be adjusted in use. In this arrangement a coverpart 15a carries the microswitch support 13, which support 13 engagesthe housing 2 by screw threads 14, and the cover part 15a is arranged sothat it can be secured to the housing 2, for example by grub screws 16engaging on the swaging of the head In. The switch is initially adjustedas above described, except that the screws 16 are loosened so that theaxial position of the cover part lSa relative to the housing 2 isadjusted to set the pin 12a in relation to the end of the piston 7, thescrews being tightened after engagement. The part 150 can slide on thehead, as shown, or engage same by screw threads, or the housing 2 asshown in FIG. 3.

The screw threads 11, 14, are of identical pitch so that the casing 10can later be adjusted in relation to the housing 2, enabling theoperating pressure to be adjusted within limits.

The switches shown in FIGS. 1 and 2 are intended to operate at pressuresup to about p.s.i. The switch shown in FIG. 3 is intended to operate athigher pressures, for example up to 500 p.s.i. The construction of FIG.3 is generally similar to that of FIG. 2, except that the cover 15a isreplaced by a housing part 17 which screw-threads on to the housing 2and also on to the casing 10. The part 17 can be locked by grub screws16a to the housing 2 after adjustment of the piston in relation to thepin 12a .As the casing 10 engages in the housing 17 by screw threads140, the spring pressure can be adjusted without upsetting the pin andpiston adjustment.

The above-described embodiments operate at supratmospheric pressure andFIG. 4 shows a construction for operation at subatmospheric pressure. Inthis construction the housing 2 engages in the flange 1a by screwthreads 18, the stub I forming the stop for the upper end of the spring9. The casing 10a is secured to the housing 2, and a plunger 19 issecured to the lower face of the diaphragm 3, the lower end of thisplunger cooperating with the pin 12a of the microswitch. The spacer ring5 and sealing ring 6 are between the parts 2 and 10a. The support 13 andeasing 10a are relatively adjustable by screw threads 14b, as are thestub flange head la which forms a casing supporting the spring andhousing 2, by the screw threads 18, so that adjustment of the distanceof the microswitch pin 12a from the plunger end, and of the springpressure on the diaphragm can be adjusted. The spring pressure can beadjusted without upsetting the switch pin adjustment or the distance oftravel of the piston.

ln all of the embodiments, in order to avoid damage to the diaphragm,the gap between the spacer ring and piston should be small and the inneredge of the ring rounded or beveled ofi'. [t is not essential for aspacer ring to be provided as the diaphragm can be clamped directlybetween the stub flange la and the housing 2. The edges of appropriateparts adjacent the piston will in this case also be rounded or beveled.

lclaim:

l. A pressure-actuated switch comprising a housing, a piston in saidhousing for axial movement therein, a diaphragm held adjacent the headof said piston, an inlet for feeding fluid pressure on to the diaphragm,a coil spring coaxial with the piston to load said piston and thediaphragm against the pressure, a support mounted on said housing, amicroswitch including an operating pin carried by said support, saidoperating pin coaxial with the piston, means for adjusting said supportaxially in relation to the piston when said switch is assembled, saidadjusting means comprising a casing screw-threaded to said housing forloading adjustment of the spring, said support engaging said casing byscrew threads so as to be axially adjustable in relation thereto, saidpiston extending through the casing for engagement with the switchoperating pin, means for limiting movement of the piston towards thepin, means for adjusting the operating pressure while said switch is inuse, said means including a cover member to which said support issecured, said cover member secured to said housing and axially movablerelative thereto, whereby said operating pin may be set in relation tothe adjacent end of said piston.

1. A pressure-actuated switch comprising a housing, a piston in saidhousing for axial movement therein, a diaphragm held adjacent the headof said piston, an inlet for feeding fluid pressure on to the diaphragm,a coil spring coaxial with the piston to load said piston and thediaphragm against the pressure, a support mounted on said housing, amicroswitch including an operating pin carried by said support, saidoperating pin coaxial with the piston, means for adjusting said supportaxially in relation to the piston when said switch is assembled, saidadjusting means comprising a casing screwthreaded to said housing forloading adjustment of the spring, said support engaging said casing byscrew threads so as to be axially adjustable in relation thereto, saidpiston extending through the casing for engagement with the switchoperating pin, means for limiting movement of the piston towards thepin, means for adjusting the operating pressure while said switch is inuse, said means including a cover member to which said support issecured, said cover member secured to said housing and axially movablerelative thereto, whereby said operating pin may be set in relation tothe adjacent end of said piston.